The present invention relates to a camera lens for a camera of fixed focal length and, more specifically, to a lens assembly for use in a digital still camera or PC camera.
Following fast development of personal computer technology, a variety of digital still cameras (DSC) have been disclosed for use with personal computers, and intensively used in families. A regular digital still camera uses a solid state image pickup device such as, charge-coupled device (CCD) or complementary metal-oxide semiconductor (CMOS), the image of an object, enabling the image thus obtained to be transferred through a data line to a personal computer, which uses a software program to convert the image into a JPEG, GIF, or TIFF file. In order to meet the tendency of the designing of digital still cameras toward microminiaturization, matching solid-state image pickup devices and related lenses are required to be as small as possible, i.e., the dimensions of the solid-state image pickup devices and the length of the lenses must be minimized. When minimizing the dimensions of a solid-state image pickup device, the overall length of the camera lens must be relatively shortened. According to conventional designs, a camera lens is comprised of a number of lenses axially aligned in a line, and an aperture arranged in between two of the lenses. Because the aperture is spaced between two lenses, the total distance of the camera lens cannot be shorted to the desired level. Furthermore, because a big number of lenses are used, the cost of the camera lens is high.
The present invention has been accomplished to provide a lens assembly, which has a simple structure and compact size. The arrangement of the lens unit greatly reduces the optical distortion, improving the image quality.
According to the primary objective as described above, the lens assembly comprises a fixed aperture, and a lens unit. The lens unit has a first lens, a second lens, a third lens, a fourth lens and a fifth lens in sequence. The first lens is a biconcave lens disposed at the front side of the lens unit. The second lens is a biconvex lens. The third lens is a biconcave lens. The fourth lens is a positive meniscus lens. The fifth lens is a positive lens having a surface, which has a larger curvature radius, facing the objective side. The first lens and the fourth lens are made of plastic having at least one of which having a non-spherical surface. The second lens, the third lens and the fifth lens are made of glass. The aperture is arranged between the first lens and the second lens.
The lens unit of the lens assembly has the conditions as described hereunder:
1.1 less than xe2x88x92f1/f less than 1.7xe2x80x83xe2x80x83(1)
xe2x80x831.1 less than f5/f less than 1.7 (2)
Wherein, f1 is the focal length of the first lens, f5 is the focal length of the fifth lens and f is the total focal length of the lens unit.
The lens unit of the lens assembly has the conditions as described hereunder: